Grease a roasting tin and place the chicken on top. Season the interior with salt, pepper and half of the rosemary. Place 2 or 3 orange pieces inside the chicken, along with 2 garlic cloves.
Place the remaining oranges all around the chicken and tuck the remaining garlic cloves under the wings and thighs. Season with salt, pepper and the remaining rosemary.
Roast in the preheated oven until the skin is nicely browned, about 15 minutes, then turn the temperature down to 180 C / Gas 4, and continue to cook until the chicken is no longer pink and juices run clear, 1 to 1 1/2 hours, depending on the size of the chicken.
If the skin is becoming too dark, cover with a sheet of aluminium foil for the last 20 minutes of roasting.